The truth is that globalisation means that the success of any individual cannot easily be attributed to any one country alone. All kinds of factors were in Joseph Schooling’s favour, for him to have achieved such spectacular success (relative to his fellow competitors).
E.g. the research conducted by scientists (non-Singaporean) that his parents / coaches relied upon, etc.
(We could easily list many more factors that are not directly related to Singapore.)
Would he have been less successful had he been the citizen of another country? That’s virtually impossible to tell.
At least, Singaporeans can be glad that we now have an Olympic Gold medallist who is happy to call Singapore (one of) his home(s).
(And he’ll be just one of many internationally successful individuals who recognise that Singapore is a great and beautiful country.)